This invention relates to a rotary fluid cylinder suitable for actuating jaws of a chuck utilized in a lathe or the like.
One example of a rotary fluid cylinder for controlling jaws of a chuck utilized in a lathe or the like is disclosed in U.S. Pat. No. 3,748,968. According to this patent, the inside of a cylinder is divided into two chambers and operating oil is alternately admitted into the chambers to reciprocate the piston so as to control the jaws of the chuck. For the purpose of preventing a decrease in the gripping force of the chuck even when the oil pressure decreases abruptly, an oil pressure lock mechanism including a check valve and a pilot valve is provided.
In the oil pressure lock mechanism, a pair of guide rods guiding the reciprocating motion of the piston in the cylinder chambers are constructed as double hollow cylinders and two annular rods are provided to extend into a hollow space between the inner and outer cylinders. One of the annular rods is formed as a spring biased check valve mechanism and the other is formed as a pilot mechanism having an oil passage through which a portion of the operating oil flows thereinto. The two annular rods are disposed to face each other in the axial direction. The inside of the inner cylinder is used as an oil passage for operating oil and is communicated with respective chambers of the cylinder via a space between the inner and outer cylinders and the oil passage in the outer cylinder. As it is necessary to communicate the space between the inner and outer cylinders of one guide rod with one of the cylinder chambers and to communicate the space between the inner and outer cylinders of the other guide rod to the other cylinder chamber, the check valve and the pilot valve should be arranged in opposite positions for each guide rod.
For this reason, in the mechanism described above, the check valve and the pilot valve are extended into the annular space between the inner and outer cylinders so that the construction is complicated and the slide resistance is large, thus requiring a high oil pressure for operating the mechanism. Moreover, due to the double wall construction, the outer diameter of the guide rod becomes large.
Moreover since the pilot mechanism comprising an annular rod formed with a pilot oil passage is disposed in a space between the inner and outer cylinders, in order to ensure necessary cross-sectional area of the oil passage of the operating oil and to increase the pilot ratio, the pressure receiving area of the annular rod must be increased. However, this increases the outer diameters of the guide rods and the cylinder so that the pilot ratio is at most 1:3 due to the construction conditions. With such low pilot ratio, response speed to the variation in the oil pressure of the operating oil becomes slow, thus requiring a long time for operating the chuck.